This is wrong, a misconception among English speaking learners of Spanish. Actually, in this case, with siempre, I think the indefinite or the perfecto compuesto are the most common options. See also here.

Because he continuously had that knowledge with him over the period of time siempre referers to. On the other hand, you may use siempre + imperfect when things happen in a discrete fashion rather than continuous: something that happened repetitively or that you used to do. For example:

Siempre supo todas las respuestas: he always had that knowledge, no matter if he actually used it or notSiempre sabía todas las respuestas: he would always know the answers

I had the exact same question when I read the same story. I suspected it might come up in a search here, and there it was!!!

Several weeks ago in my Spanish class, as we were studying the imperfect, I mentioned this exact sentence to my profesora - a Chilean native. Her explanation was that the use of the preterite in this context presumes that the person is dead. If the person is presumed to still be living the imperfect would be correct. While the person is living the knowledge is a continuing situation, requiring the use of the imperfect. But when the person dies, the period of time referred to becomes a single discrete period, starting from when he learned of it and ending at the time that he died. Because it then becomes a single discrete period of time, the preterite is then used instead of the imperfect. The same considerations also apply with conocer.

I offer that for what it is worth. This is a concept that is not intuitive to the native English speaker. Most of use are taught that saber in the preterite means to "learn of" or "become aware of", and, in the imperfect means "to know". So a construction such as this seems very confusing when the context clearly means that Nicolás always "knew". The explanation of my profesora helped me because I was certainly confused when I first read the story of Nicolás Vidal. This seems to me consistent with the comments above by others, particularly asm and Hector9.

Dear Basil Ganglia,
A very belated reply and thank you for your post to my thread!
I have also understood that the use of the preterite indicates that the person might have passed away. Recently, however, I heard on Spanish-language television a commercial for an art school and in the voice over a woman said "Siempre supe que quise ser artista". So, I wonder if there is something about the pairing of "siempre" and the preterite.
Similarly, I read another story in which a person who was still alive was described:
"Yo era un joven introvertido, pero en cambio, mi mujer siempre fue ambiciosa."
I was perplexed by the use of "fue".
I did a bit more reading about "siempre" as a time marker and verbs whose actions cannot be counted.
Actions that one can repeatedly do such as "go to the beach", "Siempre íbamos a la playa en julio" fit the traditional explanation given to English-language speakers, that siempre is associated with repeated actions in the past. However, if the action is not something for which on could count a certain number of repetitions, knowing (saber) for example, might "siempre" function less as a marker of repetition but more as a time marker that helps encapsulate the past into a completed whole?

Dear Basil Ganglia,
A very belated reply and thank you for your post to my thread!
I have also understood that the use of the preterite indicates that the person might have passed away. Recently, however, I heard on Spanish-language television a commercial for an art school and in the voice over a woman said "Siempre supe que quise ser artista". So, I wonder if there is something about the pairing of "siempre" and the preterite.
Similarly, I read another story in which a person who was still alive was described:
"Yo era un joven introvertido, pero en cambio, mi mujer siempre fue ambiciosa."
I was perplexed by the use of "fue".
I did a bit more reading about "siempre" as a time marker and verbs whose actions cannot be counted.
Actions that one can repeatedly do such as "go to the beach", "Siempre íbamos a la playa en julio" fit the traditional explanation given to English-language speakers, that siempre is associated with repeated actions in the past. However, if the action is not something for which on could count a certain number of repetitions, knowing (saber) for example, might "siempre" function less as a marker of repetition but more as a time marker that helps encapsulate the past into a completed whole?

Click to expand...

In this case I would use "quería", that "quise" is wrong there, at least to me is wrong.

If you learn the difference between imperfect and preterite WITHOUT going back and forth to your English, you will get a more solid understanding. The difference your teachers/books are telling you about SABER in the preterite and imperfect is imprecise (and imperfect ). This is the way English speakers use to understand what their own language can't. For native speaker thinking of the difference between supo and sabía, they will never conclude that one is "realized" and the other is "knew", they don't even know those verbs in English. However, the difference between these two options explain very well the issue you are trying to learn.
Juan supo que no tenía dinero. (he assumed he had some money, but later he learned that he doesn't have it anymore)
Juan sabía que no tenía dinero (he already knew about his lack of $)

Since English doesn't have these two options for the past, it is that language the one that tries to "explain" the difference.

Try to understand this without English and everything will be much easier.
Focus on the perception of time (open or closed).

Dear Basil Ganglia,
A very belated reply and thank you for your post to my thread!
I have also understood that the use of the preterite indicates that the person might have passed away. Recently, however, I heard on Spanish-language television a commercial for an art school and in the voice over a woman said "Siempre supe que quise ser artista". So, I wonder if there is something about the pairing of "siempre" and the preterite.
Similarly, I read another story in which a person who was still alive was described:
"Yo era un joven introvertido, pero en cambio, mi mujer siempre fue ambiciosa."
I was perplexed by the use of "fue".
I did a bit more reading about "siempre" as a time marker and verbs whose actions cannot be counted.
Actions that one can repeatedly do such as "go to the beach", "Siempre íbamos a la playa en julio" fit the traditional explanation given to English-language speakers, that siempre is associated with repeated actions in the past. However, if the action is not something for which on could count a certain number of repetitions, knowing (saber) for example, might "siempre" function less as a marker of repetition but more as a time marker that helps encapsulate the past into a completed whole?

I have an interesting book in my collection called Compendio ilustrado y azaroso de todo lo que siempre quiso saber sobre la lengua castellana. = anything that ever occurred to you to ask about Spanish

When we say in English "from the beginning I knew," we're not talking about ongoing states. We're saying that at a particular moment I realized something, I became aware of something. Siempre quise, siempre supe, siempre fue express the same kind of temporal setting.

It may have already been mentioned in this thread, but in the movie "Motorcycle Diaries," Che Guevara recklessly swims across a river. When he reaches the other side his companion says, "Siempre supe que podías hacerlo." I think that means I never had a moment's doubt, nothing else ever occurred to me, etc. In spite of what so many textbooks say, siempre does not always signal el pretérito imperfecto.

Just a couple of comments. I don't think repetition is necessary for the use of sabía. If someone tells me something I already know, I can say Ya sabía. If someone does something that doesn't surprise me because of their character, I might say Sabía que ibas a hacer eso. And the preterite meaning to find out (which is not something we anglohablantes have invented, as some have implied, but is what our textbooks-- which were mostly written by nativohablantes del castellano-- have told us) is supported by the fact that my Spanish-speaking ESL students often say "Yesterday I knew that (X)," when what they mean is "Yesterday I found out that (X)."

Just a couple of comments. I don't think repetition is necessary for the use of sabía. If someone tells me something I already know, I can say Ya sabía. If someone does something that doesn't surprise me because of their character, I might say Sabía que ibas a hacer eso. And the preterite meaning to find out (which is not something we anglohablantes have invented, as some have implied, but is what our textbooks-- which were mostly written by nativohablantes del castellano-- have told us) is supported by the fact that my Spanish-speaking ESL students often say "Yesterday I knew that (X)," when what they mean is "Yesterday I found out that (X)."

Try to understand this without English and everything will be much easier.
Focus on the perception of time (open or closed).​

In the sentence “I believed that Juan was dishonest,” the imperfect would be used, correct? Is that because the implication is that I had the belief for a period of time but the time period is of unspecified duration?

In the sentence “I always believed that Juan was dishonest,” based on the discussion in this thread, I assume it would take the preterite. Would it?

The "always" here implies that I believed it over a complete time period, but I'm not clear what time period is implied. It's not a case where my life is over, as was the case with Nicolás Vidal (original post). It's not a case that I believed it all my life, like Hector9's football player, Marcos (post # 3). Is it because it implies that for the entire time that I knew Juan I believed that he was dishonest. Or that for the entire time that I thought about the issue of whether Juan was honest or not, I believed that he was dishonest? Or is it something else? Or does it not matter exactly what the time period is because the implication is that whatever time period I have in mind, it was a continuous belief?

I originally used the word "knew" in my examples (and then changed it) because I was thinking of the context in which I say it after I receive proof of Juan's dishonesty. Since I didn't have proof before, my saying that I "knew" it was really a statement of belief.

But let's change the context and say that I had actual knowledge of Juan's dishonesty because I saw him lie and steal. Later someone says to me, "Did you know Juan was a liar and a thief?" Since I did know that, my answer is that "I knew Juan was dishonest." Is that in the preterite or the imperfect? From the time I saw him lie and steal, I continuously knew he was dishonest. But no time period is stated or implied.

If my answer is that "I always knew Juan was a dishonest," would my statement would use the preterite because a continuous knowledge over a time period is implied?

But let's change the context and say that I had actual knowledge of Juan's dishonesty because I saw him lie and steal. Later someone says to me, "Did you know Juan was a liar and a thief?" Since I did know that, my answer is that "I knew Juan was dishonest." Is that in the preterite or the imperfect? From the time I saw him lie and steal, I continuously knew he was dishonest. But no time period is stated or implied.

Click to expand...

Sabía que Juan era dishonesto - I had a hunch or I actually had the knowledge because I caught him doing something dishonest.

Supe que Juan fue dishonesto - I found out that or at that moment I caught him doing something dishonest.